Brila Energy chairman Rowaye Jubril says the pirates discharged the vessel's entire cargo,about 5,000 tons of fuel, while the 16 crew members were locked in the ship's dining room.
Ivorian port officials say the tanker was seized late last week as it prepared to unload at the port in Abidjan, the country's commercial capital.
It is unclear where the tanker was released, but officials say it was last located off the coast of Ghana.
Hijackings and attacks on ships have increased along Africa's Gulf of Guinea in the past year.
The International Maritime Agency says piracy in West Africa, particularly in the Gulf of Guinea, is on the rise with 58 incidents reported in 2012, including 10 hijackings and 207 crew members taken hostage.
A total of five incidents were reported off Ivory Coast in 2012, up from one the previous year. In October, suspected Nigerian pirates seized a tanker carrying more than 30,000 tons of gasoline off the coast of Abidjan, the first reported hijacking in the country.